A network of this type is the subject matter of my copending application, Ser. No. 404,236, filed Aug. 2, 1982. Microwave energy reflected by a target and incident on a radar antenna along a main lobe of its radiation pattern may be encumbered by interfering radiation from one or more jammers picked up along side lobes of that pattern. The superimposition of the interfering signals upon the incoming echoes creates disturbances in the evaluation of the echoes which may disorient the radar relatively to a target being tracked or searched for.
In the case of a mechanically scanning antenna it has already been proposed to suppress these interferences by the provision of ancillary antennas flanking the main antenna and participating in its scanning motion, these ancillary antennas being oriented along the side lobes of the main radiation or beam pattern from which interfering signals are received. The associated processor, in its receiving section, treats the collateral signals emitted by these ancillary antennas as representative of estimated disturbance and subtracts them from the raw output signal of the main antenna to produce a useful signal purged to a greater or lesser degree from these interferences.
This mode of operation, which reduces the gain of the main antenna in the directions of incidence of the interfering radiation, requires a number of ancillary antennas at least equal to the number of jammers whose signals are to be suppressed, along with as many auxiliary channels in the processor in which the collateral signals from the ancillary antennas are properly weighted. The same technique can be used in the case of an electronically scanning main antenna with a phased array of elemental radiators whose individual output signals are weighted by phase shifters in the principal channel of the processor, in conformity with the sweep of the radiation pattern, as is-well known in the art.
A drawback of the method just described is the fact that the ancillary antennas have their phase centers necessarily offset from that of the main antenna by a distance greater than half the width of the effective area in which the desired incident radiation is being collected by a rotating reflector or by the array of elemental radiators. This offset, more fully discussed hereinafter, decorrelates the interfering signals processed in the principal and auxiliary channels so as to impair the suppression of the resulting disturbances.
With an electronically scanning antenna the disturbances could also be spatially filtered out by modifying the weighting coefficients for the output signals of all the elemental radiators so as to reduce the antenna gain in the suspected direction or directions of incidence of the jamming signals. This latter method, while more effectively suppressing the interferences, is rather cumbersome since it requires individual processing channels and weighting circuits for all the elemental radiators.